The present invention relates to a method for improving the performance of a cryogenic heat exchanger under frosting conditions, and more specifically to a method suitable for a precooler of an air breathing engine.
In order to realize a liquid air cycle engine or a precooled turbojet engine, the development of a high-performance precooler is a key technology. The foremost concern in the development of such a precooler is frost formation on the heat transfer surface of the heat exchanger.
When frost is formed on a heat transfer surface, the efficiency of heat transfer decreases due to the thermal resistance of the frost layer. Further, the flow path of the main air flow narrows, and the pressure loss of the flow increases. The frost layer formed on the heat transfer surface in a cryogenic state has a low density and a low thermal conductivity, and therefore the performance of the heat exchanger is greatly influenced.
In case of the precooler of an air breathing engine used for a space craft, the frost formation creates a trouble particularly when it is flying at low altitude, which is in the acceleration phase. During this period (about several tens to several hundreds of seconds), the operation of the engine cannot be stopped. Therefore, a defrosting cycle, which is applicable in the heat exchanger used for refrigeration or air-conditioning, cannot be applied.